1. Field of the Invention
This invention relates to an improved keyless drill chuck.
2. Description of the Prior Art
Prior art drill chucks, used both commercially and by hobbyists, have generally required the use of a separate key for adequately tightening the gripping jaws of the chuck against a tool shank, such as a drill bit, in order to insure that the bit does not slip relative to the chuck during a drilling operation. It has long been felt, however, that the use of a separate key was both annoying and inconvenient. That is, the tightening of the drill chuck is a cumbersome operation which wastes valuable time. Also, if the key is lost, the drill cannot be used. Further, the key used with one drill chuck is not necessarily interchangeable for use with other drill chucks of different manufacture. Still further, it has long been recognized that to insure uniform gripping of a bit of each of the jaws of a chuck, the key must be progressively positioned and rotated adjacent to each succeeding gripping jaw. This particular method of operation is often overlooked, with resulting slippage, off-center gripping and scoring of the bit.
To overcome the inherent deficiencies of key-type drill chucks, attempts have been made at constructing a keyless drill chuck. However, these prior art attempts have failed for a number of reasons, for instance, the relative complexity of the design, the inability to obtain adequate gripping force on the bit, the difficulty encountered in attempting to release the bit from the drill chuck after the drilling operation is completed and the inability to accurately grip the bit in a central position. Further, many of the prior art keyless drill chucks are operative in only one direction, and, as a result, these drill chucks are not useable with reversible drills.
Kirkland, U.S. Pat. No. 2,220,654, is an example of a prior art keyless drill chuck. The chuck in this patent includes a sleeve having a shoulder, a cam bushing being received within the sleeve and abutting the shoulder, a core member having a plurality of axially directed slots and a threaded portion, and a plurality of tapered rollers positioned within the axially directed slots. The core member and tapered roller assembly are received within the cam bushing and a driving member is threadably received by the core member threaded portion. The tapered rollers are retained within the axially directed slots by a reduced clearance portion formed on an inner part of each slot. The chuck utilizes a pin fixed to the sleeve and received within a steep pitch slot in the core member for rotating, thereby axially moving the core member relative to the driving member, and the driving connection between a drive motor and the tool is through the threaded connection between the driving member and the core member.
Some disadvantages of this chuck are (1) the size of a tool that can be inserted within, or held by, the core member is limited by the dimensions of the core member and by the reduced clearance portion formed on the inner part of each slot in the core member; (2) since the driving connection is through a threaded fitting, the chuck is useable only in a single rotary direction; (3) the tapered rollers are not biased to an open equally spaced position; (4) the sleeve fixed pin and the driving connection between the drive member and the tool are through a threaded connection; and (5) an anti-friction thrust bearing is not provided for assisting the circumferential movement of the tapered rollers along the tapered bore with a planetary action.
Kirkland, U.S. Pat. No. 2,069,527, discloses a keyless chuck in FIG. 8 which includes a multi-directional driving member having both a tapered bore and varying radius cam surfaces. Received within the tapered bore is a spring-biased core member. The core member is provided with a plurality of axially directed slots in which are located a plurality of tapered gripping rollers. The rollers are retained within the axially directed slots by a reduced clearance portion formed on an inner part of each slot. A gauge sleeve is provided threadably engaged with matching threads on the outer circumference to the driving member. The gauge sleeve acts against the core member for forcing the tapered gripping rollers into the tapered recess of the driving member.
Some disadvantages of this chuck are (1) the reduced clearance portion formed on the inner part of each slot permits the chuck to be used for holding tools of only a single diameter; (2) the tapered rollers are not biased to an open equally position; (3) an anti-friction thrust bearing is not provided for assisting the circumferential movement of the tapered rollers along the tapered bore with a planetary action.